Hydrocarbon oil-containing sludges of various types and consistencies are commonly produced in oil production and extraction processes, especially in the production of heavy oils and in the extraction of shale oils and oil sands when using aqueous extraction processes. They may also be produced as a result of hydrocarbon oil spillage onto soil etc.
A typical example of a hydrocarbon oil-containing sludge is that produced as a by-product of oil sands extraction. The heavy oil or bitumen from oil sands is commonly extracted using a hot water process. In situ techniques, including enhanced oil recovery, are now also being used to exploit oil sands deposits which are too deep to be economically mined. These in situ techniques commonly adopt steam flood, fire flood, carbon dioxide injection and oxygen injection. The production fluid recovered from the reservoirs is a mixture, usually a more or less tight emulsion, of water, solids and hydrocarbon. The product emulsion is broken by further treatment, e.g. in washtanks, settlers, heater treaters, electrostatic dehydrators and the like. From these treatments, there are recovered two streams, a useful hydrocarbon oil stream and the tailings. Tailings consist of water and solids contaminated with hydrocarbon. Normally, the tailings are collected into a pit or pond, in which the solids settle to the bottom and some water and hydrocarbon are recovered from the top. The settled solids form a sludge, which still contains a substantial amount of hydrocarbon and represents an environmental hazard. Disposal of the sludge presents economic and environmental difficulties. Adding to the disposal problem is the fact that the sludges are not stable over the long term.